Biomechanical appraisal of some skeletal features associated with head balance and posture in the Hominoidea.

The condylar position index, condylar angle and the area of insertion of the nuchal musculature corrected for condylar position, direction of muscle pull and skull size were determined in Homo sapiens, Gorilla, Pan and the casts of two Neanderthal and two australopithecine crania. In all three attributes, the values of H. sapiens exceeded, by statistically significant amounts, those for the ape genera. The greater value for the condylar position index indicates a better balance of the head, that for the condylar angle reflects the more vertical orientation of the vertebral column while that for the corrected nuchal area suggests a less effective nuchal musculature in H. sapiens as compared to the apes. In the casts of the Neanderthal crania, the values all came within, or close to, the ranges for H. sapiens. In the australopithecine casts, the condylar angle cane within the ranges for H. sapiens while the condylar position index and the corrected nuchal area were intermediate in value between H. sapiens and the extant apes. These findings are consistent with observations from other skeletal regions that while Australopithecus had an upright posture, this creature was, in the complex of posturally significant morphological features, distinct from extant hominoids.